Local weather affects body condition of three North American songbird species on the Texas Coast

Abstract Body condition is a frequently used physiological indicator of avian health and can be affected by an array of environmental variables. Although a number of studies have investigated the specific effects of individual weather variables on body condition in birds, few have analyzed the effects of both temperature and precipitation within the context of an extreme weather event such as hurricanes. In this study, we examined the relationship between breeding‐season body condition and daily maximum temperature, daily minimum temperature, and monthly total precipitation for three passerine bird species at the Welder Wildlife Refuge near Rockport, Texas. We also evaluated yearly changes in body condition over a 12‐year period for northern cardinals (Cardinalis cardinalis), painted buntings (Passerina ciris), and white‐eyed vireos (Vireo griseus), focusing on the extreme precipitation event of Hurricane Harvey, which caused heavy localized flooding. We found that body condition declined with average daily minimum and maximum temperatures, while precipitation had varied, species‐specific effects in the three species analyzed. Our results also suggest that northern cardinals experienced a notable reduction in average body condition in the 2 years following Hurricane Harvey. Taken together, we conclude that short‐term precipitation and temperature drivers can be important correlates of body condition in songbirds and that severe weather events may reduce body condition in some bird species.

as a functional indicator for entire ecosystem health (Bregman et al., 2016;Smits & Fernie, 2013) and birds are valuable providers of ecosystem services (Sekercioglu, 2006). As bird populations decline, negative effects on these ecosystem services and their resulting value to human societies may occur (Sekercioglu et al., 2004).
Responses to hurricanes and other natural disasters can be studied in birds in numerous ways (Coppedge et al., 2008;McCloy et al., 2022;Sigel et al., 2006), including through species diversity (Blair, 1996), community assemblages (Crooks et al., 2004), population dynamics (SAEther et al., 2004), and individual physiology (Schoech et al., 2011). Body size along with body mass adjusted for size (i.e., body condition) are two physiological measures that are easily measured in the field by practitioners and may provide insight into sublethal effects of disturbance on individuals and populations. Body condition is a useful indicator of disease prevalence, individual health, and fitness in vertebrates including birds (Granthon & Williams, 2017;Stevenson & Woods, 2006), bison (Vervaecke et al., 2005), and some reptiles (Romero et al., 2001). Body size can reflect early-life stressor experiences (Grace et al., 2017;Schoech et al., 2011). In songbirds, both measures are responsive to climate change and acute disturbance events (McLean et al., 2018). For example, climate change is correlated with a decrease in body condition, fat scores, and longer average wing lengths in several species (Collins et al., 2017;Van Buskirk et al., 2010).
Hurricanes are often accompanied by sudden extreme increases in precipitation, which are expected to become more intense, globally, with continued climate change (O'Gorman, 2015). In migratory songbirds, the links between winter rainfall and/or habitat moisture, food availability, and body condition are well established (e.g., Akresh et al., 2019aAkresh et al., , 2019bAngelier et al., 2011;McKinnon et al., 2015;Studds & Marra, 2007). In general, decreased precipitation on the wintering grounds drives decreases in food availability, which then leads to decreased avian body condition (e.g., McKinnon et al., 2015, Smith et al., 2010, Studds & Marra, 2007 that can carry over to impact reproductive success during the breeding season (Rockwell et al., 2017). Relationships between body condition and precipitation on the breeding grounds are also evident in the literature. For some species, increased precipitation is positively correlated with body condition until a threshold is reached, after which body condition declines (e.g., male great snipe, Gallinago media, Witowska et al., 2022). For others, precipitation during the breeding season is negatively correlated with fitness measures including reproductive success, juvenile survival, and parental survival (e.g., northern wheatear, Oenanthe oenanthe, Öberg et al., 2015, grassland birds, Zuckerberg et al., 2018, wire-tailed manakin, Pipra filicauda, Ryder and Sillett 2006, due in part to declines in parental nest visitation rates (Öberg et al., 2015) along with flooding and patch-specific variation in microclimates (Zuckerberg et al., 2018).
Shifts in larger-scale precipitation patterns are also linked to variation in natural selection on birds (Siepielski et al., 2017), indicating that precipitation changes have the potential for long-term impacts on populations.
In addition to precipitation, other mechanisms can influence the effects of hurricanes on birds. For example, high wind speeds in conjunction with extreme precipitation may cause direct mortality of birds (Michener et al., 1997), and destruction of avian habitat and food resources (Wiley & Wunderle, 1993). These effects are typically strongest within the year after a hurricane, although population dynamics may be altered for years afterward (Michener et al., 1997). The strength of indirect effects on avifauna are mediated by numerous species-specific and ecological factors, including the specificity of vegetative reliance, foraging guild, endemic status, and seasonal timing of the hurricane. Species that rely on specific vegetation structures for foraging, hunting, or nesting often experience short-term decreases in population size following a hurricane due to limited food availability and reduced cover while species with broader vegetative relationships are largely unaffected (Wiley & Wunderle, 1993). Species with granivorous, nectivorous, and frugivorous dietary preferences may be more negatively affected by hurricanes than insectivorous species, because of the quick posthurricane recovery time of many insect populations, coupled with the high level of dietary specialization for many granivores, nectivores, and frugivores (Ackerman et al., 1991;Askins & Ewert, 1991). Finally, breeding-season disturbances oftentimes have the greatest long-term effects on populations due to the vulnerability of juvenile and adult populations at these times (Michener et al., 1997).
In this study, we sought to elucidate how the body condition of three passerine bird species near Rockport, Texas responded to changes in temperature and precipitation, particularly in the three breeding seasons following the extreme precipitation event of Hurricane Harvey. Hurricane Harvey made initial landfall on August 25, 2017, as a Category 4 hurricane just east of Rockport on the northern end of San Jose Island. The hurricane then made a second landfall on the northeast side of Copano Bay several hours later. Hurricane Harvey had the highest storm-total precipitation ever recorded in the United States and its economic cost was second to only Hurricane Katrina (Blake & Zelinsky, 2018). The impact of Hurricane Harvey in the immediate vicinity of our study location provided a unique opportunity to analyze site-specific shifts in avian body condition in subsequent years.
We generated a series of hypotheses concerning the effects of age and various weather variables, predicting a differential response across species. First, we hypothesized (H1) precipitation would have a positive effect on scaled mass index of northern cardinal (Cardinalis cardinalis; resident) and painted bunting (Passerina ciris, migrant), only up to a certain threshold. These species maintain at least a partially granivorous diet (Billerman et al., 2022) and low precipitation totals may decrease seed production, while an overabundance of precipitation may cause flooding and destroy seed-producing vegetation (Oram et al., 2021). We also predicted that (H2) minimum temperature would have a positive effect and maximum temperature would have a threshold effect on the scaled mass index of these two species, as seed production may be affected by extreme temperatures. Lastly, we hypothesized (H3) that the scaled mass index of white-eyed vireo (Vireo griseus, migrant), which is largely insectivorous (Hopp, 2022), will be positively affected by precipitation and minimum temperature up to a certain threshold, but negatively affected by maximum temperature because insects are highly sensitive to changes in temperature and precipitation (Ma et al., 2021;Møller, 2019;Rebaudo et al., 2016). Additionally, migrant species such as the white-eyed vireo and painted bunting may demonstrate higher variation in body condition due in part to spillover effects from conditions on the wintering grounds (Akresh et al., 2019a;Rockwell et al., 2017).

| MATERIAL S AND ME THODS
We analyzed 13 years of data from the Monitoring Avian Productivity and Survivorship (MAPS) banding station at the Welder Wildlife Refuge, using scaled mass index to identify changes in body condition among three avian species in relation to year, precipitation, and temperature. Scaled mass index is a condition index calculated using both body mass and morphometric measurements (i.e., wing length) to assess overall body condition (Peig & Green, 2009). Condition indices have long been used in studies of avian physiology, and the use of multivariate measures is recognized as the most accurate means of doing so (Freeman & Jackson, 1990). A variety of methods exist for quantifying avian body condition through condition indices, and there is still ongoing debate as to which method is generally the "best" (Akresh et al., 2019a;Labocha et al., 2014). Here we chose to use scaled mass index (Peig & Green, 2009), which is an effective and wellregarded measure of body condition in birds (Danner et al., 2013;English et al., 2018;Peig & Green, 2009). Scaled mass index has previously been shown to perform better than numerous other condition indices because it uses a multiplicative error function, which better accounts for the scaling between mass and body length in an individual over time (Danner et al., 2013;Peig & Green, 2010).  (2) to avoid additional bias caused by incorporating multiple capture locations into this analysis.

| Data collection
Banding operations were carried out between the years 2007 and 2019 following standardized MAPS protocol established by the Institute for Bird Populations. The complete and current version of the MAPS protocol is described in DeSante et al. (2015), with an abbreviated description provided, here. Between 10 and 11 mist nets were operated for 1 day in each 10-day period during the breeding season (May to August) for up to 6 h following sunrise (i.e., highest bird activity) (Robbins, 1981). At the Welder Wildlife Refuge, mist nets were typically operated for only 3-4 h postsunrise due to rapidly rising temperatures in conjunction with very high humidity levels. Once temperatures reached 90 degrees Fahrenheit, the nets were closed for the day to ensure the safety of any birds captured. Each mist net was 12 m long and 2.5 m tall with a 30 mm mesh. Nets were checked every 20-30 min throughout the period in which they were open. All birds captured were identified to species, sex, and age based on Pyle (1997)

except for unidentified migrant
Empidonax genus flycatchers. Birds were banded with a nine-digit aluminum band from the U.S. Geological Survey, and wing and mass were measured. Data were recorded in the field on paper datasheets and subsequently entered into MAPSPROG, the dedicated database for storing all MAPS data from stations across the US, where they were proofed and checked for quality. Data were then formatted in Microsoft Excel and statistical analyses were performed in R (v 4.2.1; R Core Team, 2021).
We downloaded weather data from DayMet (Thornton et al., 2021) using the Single Pixel Extraction Tool. This provided a 1 km 2 resolution of surface weather data from a given set of coordinates. Then, we analyzed total precipitation, average maximum temperature, and average minimum temperature for the 30 days prior to the capture of each individual bird. For example, if an individual bird was captured on 15 May, weather data for that bird was collected for the period between 16 April and 15 May. Hurricane Harvey made landfall in August 2017, which fell outside the temporal window of the MAPS protocol. Thus, avian data was not collected in the 30 days immediately following the hurricane impact and subsequent data was collected beginning in May 2018. We chose to analyze these temperature and precipitation variables for two main reasons: first, these data were readily available on a fine spatiotemporal scale. Second, the existing literature allowed us to make a priori predictions (Gardner et al., 2018) about their effects on avian body condition. Despite their availability in DayMet, we did not include additional weather variables such as wind, relative humidity, and solar radiation to minimize the risk of overfitting our models, and because we predicted a priori that these variables would not have notable effects on avian body condition.
Effects of weather on animals can vary temporally (English et al., 2018;Salewski et al., 2013), and therefore, we carefully considered the time frame of weather variables we selected. We chose to use a 30-day time frame with the intent to capture short-term effects of extreme weather (such as dehydration due to high heat) alongside effects due to longer-term changes in resource availability.

| Scaled mass index calculation
We calculated scaled mass index for each species using the following equation: where M i is scaled mass index value, M i is body mass, L 0 is average population wing length calculated across all years, L i is wing length, and b SMA is the scaling exponent, calculated as the slope of the Standardized Major Axis (SMA) regression line across ln-transformed data of M i and L i (Peig & Green, 2009). This was calculated in JMP Pro (v. 14.0.0) using a bivariate fit of the ln of mass to the ln of wing length and then calculating an orthogonal fit ratio (SMA regression line). We calculated scaled mass index values across sex for each species in this study because the relationship between size and mass did not differ significantly between sexes.

| Statistical analyses
We analyzed the scaled mass index of the three most frequently We constructed a series of nonparametric generalized additive models (GAMs; Gaussian, identify link function) with the "mgcv" package (Wood, 2011) in the R statistical programming language (v 4.2.1; R Core Team, 2021) to evaluate the effects of selected variables on avian body condition. Unlike generalized linear models or linear mixed effects models, GAMs do not make a priori assumptions about the relationship between variables. Their effects are additive, and smooths are fitted with smoothing splines by cubic  (Wood et al., 2014;Yee & Mitchell, 1991). We estimated the degree of smoothness of model terms through a maximumlikelihood approach, which allows each term to be penalized to zero (Viana & Chase, 2022

| Weather variables
Average daily minimum temperature was included in the top models predicting body condition for northern cardinal and white-eyed vireo, but not painted bunting. For both species scaled mass index increased with minimum temperature, although for white-eyed vireo this positive effect only lasted until 13 degrees Celsius, after which scaled mass index declined with minimum temperature (Figure 2).
The 95% CIs and 85% CIs both did not overlap with zero for either species, although the lower 95% CI closely approached zero (9.22e-03) for the white-eyed vireo (Table 3).
Average daily maximum temperature was a predictor in the top models predicting scaled mass index for northern cardinal and painted bunting. We found a generally negative relationship between average daily maximum temperature and scaled mass index for both species (Figure 3). For northern cardinal, the 95% and 85% CIs did not overlap with zero. However, for painted bunting the lower 95% CI (5.44e-43) and lower 85% CI (1.31e-32) both closely approached zero, suggesting a weaker effect (Table 3).

| Age and sex
The effects of age and sex were present in the selected models for northern cardinal and painted bunting. However, we only found age to be an important predictor of scaled mass index for northern cardinal (p < .001), such that hatch year, or juvenile, individuals had higher scaled mass index scores than adults (

| Year
The effect of year was only present in the top model predicting scaled mass index for northern cardinal. Despite this, there was no significant effect of year on scaled mass index (Table 4).
However, we also performed a series of one-sample t-

| DISCUSS ION
Previous literature suggests a complex and dynamic response of avian body condition to weather-related variables (Gardner et al., 2018), which is consistent with the results of our study. At our long-term study site on the Texas coast, we found that average daily maximum and minimum temperatures and total precipitation in the prior month were associated with changes in passerine body condition during the breeding season. Our results suggest nonlinear responses to these variables for some species, including threshold effects for both temperature and precipitation, after which associations between weather and body condition reversed. Overall our results indicate that temperature and precipitation can act as important drivers of avian body condition at a local scale, which is also consistent with prior studies focused on nonavian taxa (e.g., springbok; Turner et al., 2012, and kangaroos;Plaisir et al., 2022).

| Weather parameters
We found associations between body condition and all weather variables for the species in this study, although the directions of those effects were not easily explained by diet, as we predicted. All species displayed a positive effect of precipitation on body condition at low to moderate levels of precipitation. However, that effect peaked around 14 cm of total precipitation for two of the three species (i.e., white-eyed vireo and painted bunting), and then reversed.
This threshold effect may be due to destruction of cover and food sources because of flooding, and the subsequent displacement of birds (Knutson & Klaas, 1997). Since it is widely established that declines in food availability may lead to declines in avian body condition (McKinnon et al., 2015;Smith et al., 2010), it is possible that the more generalist diet of northern cardinals provided some protection from the potential destructive effects of very high levels of precipitation.
Average daily minimum temperature had a positive effect on scaled mass index of northern cardinal and white-eyed vireo, although the latter again displayed a threshold effect around 13 degrees Celsius after which minimum temperature had a strongly negative effect on body condition. Increasing minimum temperatures may generally correspond with increased food availability, although very warm minimum temperatures may inhibit insect emergence (Abarca & Spahn, 2021), thus decreasing body condition of the insectivorous species such as the white-eyed vireo.
Alternatively, the smaller-bodied white-eyed vireo may be more strongly affected by thermoregulatory requirements at lower minimum temperatures than northern cardinals, necessitating increased fat stores and lower activity levels (Stevenson & Woods, 2006).
Average daily maximum temperature was negatively associated with scaled mass index of both northern cardinal and painted bunting, as we predicted, although these effects were weaker for painted bunting. We suspect that this pattern is driven by increasing physiological thermoregulatory stress in individuals as temperatures rise (du Plessis et al., 2012), and/or potential declines in food availability under high heat conditions.
The presence of numerous models with Δ AICc < 2 for northern cardinal, painted bunting, and white-eyed vireo suggests that the weather variables in our analyses were explaining similar amounts of variation in the dataset, and there was no single weather variable that most strongly explained changes in body condition of these species. For white-eyed vireo, the null model had a Δ AICc of 1.892, indicating that weather variables only weakly explained variation in scaled mass index for this species and that variation in body condition may be largely driven by nonweather factors or by weather across larger or smaller temporal windows.

| Year
Our results indicate that scaled mass index values for northern cardinals in the two breeding seasons following Hurricane Harvey (2018 and 2019) were significantly lower than in previous years ( Figure 5). While we were unable to test direct causation due to the correlative nature of this study, a relationship with Hurricane Harvey seems probable due to the strong impact of the storm in this region (Blake & Zelinsky, 2018) and the possibility of the hurricane affecting food resource availability. Other studies have reported higher variance in body condition following high precipitation because of increased nestling survival (Zuckerberg et al., 2018), which could result in lower mean body condition.
However, this is unlikely in our case because our precipitation results indicate a generally positive effect of precipitation on body condition for northern cardinals, and Hurricane Harvey probably did not directly affect nestlings because it occurred after the breeding season, although it may have affected fledglings (Lowther et al., 2020

| CON CLUS ION
Taken together, our results demonstrate that variation in avian body condition is associated with local temperature and precipitation patterns and that severe weather events may have multiyear impacts on body condition for some species. Body condition is associated with individual fitness for many vertebrate taxa, including birds (Stevenson & Woods, 2006), reptiles (Romero et al., 2001), and mammals (Vervaecke et al., 2005). Reduced body condition can negatively affect foraging success (Jakob et al., 1996) and increase susceptibility to disease and predators (Kouba et al., 2021). Thus, our observed impacts of short-term weather and an extreme weather event on body condition may have broad implications for individual fitness and population stability (Schoech et al., 2011), although currently, relationships between body condition, climate change, and population dynamics are unclear (see McLean et al., 2018). This is a topic that should be investigated in future studies. Furthermore, since the MAPS program is only run during the primary avian breeding season (May-August), any changes in body condition during other months were not analyzed in this study but could also have important impacts on fitness (Stevenson & Woods, 2006).
Our results also highlight the importance of nonlinear effects of weather, such as threshold effects, for many species. As climate change increases the probability of extreme weather events (Bregman et al., 2016) and continues to impact bird communities (Jenouvrier, 2013), we expect species to be pushed beyond these thresholds more frequently. We also note that these associations between weather thresholds and body condition will likely vary regionally. For example, daily maximum temperatures at our study site between May-August already frequently approach or exceed the point in which northern cardinal body condition declines most steeply in our study (approximately 30 degrees Celsius).
In general, the three species in our study were at greatest risk of low body condition at low minimum temperatures and high maximum temperatures. However, there was large speciesspecific heterogeneity in these responses, especially in regard to precipitation. This suggests that responses of avian body condition to weather may not be easily generalized across species, even for passerine species located in the same small geographic area.
Future research across a broader spatial scale (e.g., the southeastern United States) may provide further insights as to how local and regional bird populations continue to respond in the years following extreme weather events. Finally, localized studies should also evaluate the effects of weather and reduced body condition on survival and reproductive success. This manuscript is Welder Contribution Number 737.